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I am a climate dynamicist with broad interests in the diagnosis, modeling, and predictability of large-scale weather and climate variations around the globe on time scales of days to centuries. Our team is engaged in documenting and understanding the regional aspects of ongoing climate changes, especially changes in extreme weather statistics, and determining to what extent they are anthropogenic or consistent with natural climate variability. We are also interested in documenting and understanding the actual as well as potential skill of weather and climate predictions, which is inherently limited due to the chaotic nature of the system, and how the current prediction systems need to be improved to achieve the potential skill.

Current Research

Changing risks of extreme warm spells are not being determined by mean warming alone

It is generally presumed that global warming has increased and will continue to increase the likelihood of extreme warm temperatures almost everywhere on the globe. We find, however, using three very different types of observational datasets and model simulations of the 1959 to 2012 period that this is generally not true. While extreme warm spells indeed became more common in many regions, in many other regions their likelihood remained almost the same or even decreased from the first half to the second half of this period. The basic reason for this was a decrease of temperature variability in such regions that nearly offset and in some cases even negated the effect of the mean temperature shift on extreme temperature probabilities. The consistency of these changes among the different observational datasets and model simulations examined suggests that they are robust regional aspects of global warming associated with atmospheric circulation changes. This highlights the need for climate models to represent not just the mean regional temperature signals but also the changes in daily temperature variability associated with global warming to correctly project the changing risks of extreme hot spells into the future. (Sardeshmukh, Compo, McColl, and Penland)

Change from 1959-85 to 1986-2012 of the statistics of 5-day averaged lower tropospheric (850 hpa) temperatures in the December through February season. Change in mean (deg C, left column), standard deviation (deg C, middle column), and in the probability of exceeding an absolute extreme warm temperature threshold (defined at each location as the mean plus 2.5 standard deviations in the 1959-85 period). Results are shown for (top row) the JRA55 reanalysis dataset, (middle row) the 20th Century Reanalysis version 2c dataset, and (bottom row) an ensemble of global atmospheric general circulation model simulations with prescribed observed time-varying sea surface temperatures and sea ice and radiative forcings. Stippling shows regions where the change in the probability of extreme warm spells (A+) was less than expected from the change in the mean temperature alone (< 0.001).